1. Field of the Invention
The invention relates to a check valve of the so-called "duckbill" type for use in sewage treatment systems.
2. Description of the Prior Art
EPA directives and studies on aeration of sewage direct attention to the fact that one of the simplest, most inexpensive methods of cleaning up or partially cleaning sewage is to aerate it with either oxygen or air.
There are many plants worldwide that clean or partially clean sewage by aeration. There are many products to allow air into the process. Sewage is processed in a very large tank, known as an "aeration tank". At the bottom of this tank are many devices allowing air to float through sludge and sewage. One such device is a porous or perforated ceramic dome. A problem with this dome is that algae grows on the dome and blocks the holes.
There are many other companies that make a network of piping with valves that allow air to bubble through the system. When the air is shut off, the sludge must be prevented from backing in and plugging the holes. Therefore, a check valve is required. Generally speaking, the sludge and raw sewage in the aeration tank is 3 feet deep. In other cases, however, the sludge is 10 feet deep which requires larger, high volume check valves to overcome the head pressure.
The check valve should be maintenance free. Currently, there are many metal check valves on the market. However, the filthy sludge and sewage clogs, packs, jams, and generally makes the metal valves inoperative. An elastomeric check valve, constructed from a material such as rubber, would operate trouble free.
The customer wants to know the volume and pressure of the air being introduced into the sewage. It would be advantageous to provide the check valve with a predetermined orifice size and an arrangement to allow a very exact quantity of air into the system.